How can the default save format be changed for OS X Preview app?

Question

Is there a resource showing all the possible syntax for changing the preference file for the preview app in os x? I'm using Catalina if that matters. I frequently copy an image to the clipboard and then command N in preview and then want it to save in PDF format instead of the default PNG format.

defaults write com.apple.Preview

Answer 1

Unless you need to edit the image in Preview, I'd suggest leaving it out of the equation altogether.

I use the following python script which saves any image on the clipboard to a PDF file, using a save dialog. (If the file exists, it adds the image as a new page.) You can embed it in an Automator workflow with a Run Shell Script action, or add it to the /Library/Scripts folder, and you can access it using the Scripts menulet. (Script Editor.app Preferences enable the menulet.)

#!/usr/bin/python

from AppKit import NSPasteboard, NSPasteboardTypePDF, NSPasteboardTypeTIFF, NSPasteboardTypePNG, NSTIFFPboardType, NSPICTPboardType, NSImage, NSSavePanel, NSApp
from Foundation import NSURL
import Quartz as Quartz
import os, syslog

def save_dialog(directory, filename):
    panel = NSSavePanel.savePanel()
    print (panel)
    panel.setTitle_("Save clipboard")
    myUrl = NSURL.fileURLWithPath_isDirectory_(directory, True)
    panel.setDirectoryURL_(myUrl)
    panel.setNameFieldStringValue_(filename)
    NSApp.activateIgnoringOtherApps_(True)
    ret_value = panel.runModal()
    if ret_value:
        return panel.filename()
    else:
        return ''

def main():
    destination = os.path.expanduser("~/Desktop/")
    outfile = save_dialog(destination, "Clipboard.pdf")

    myFavoriteTypes = [NSPasteboardTypePDF, NSPasteboardTypeTIFF, NSPasteboardTypePNG, NSTIFFPboardType, NSPICTPboardType, 'com.adobe.encapsulated-postscript']
    pb = NSPasteboard.generalPasteboard()
    best_type = pb.availableTypeFromArray_(myFavoriteTypes)
    if best_type:
        clipData = pb.dataForType_(best_type)
        if clipData:
            image = NSImage.alloc().initWithPasteboard_(pb)
            if image:
                page = Quartz.PDFPage.alloc().initWithImage_(image)
            if os.path.exists(outfile):
                pdfURL = NSURL.fileURLWithPath_(outfile)
                myFile = Quartz.PDFDocument.alloc().initWithURL_(pdfURL)
                if myFile:
                    pagenum = myFile.pageCount()
                    myFile.insertPage_atIndex_(page, pagenum)
                    print ("Image added to Clipboard file.")

            else:
                pageData = page.dataRepresentation()
                myFile = Quartz.PDFDocument.alloc().initWithData_(pageData)
            myFile.writeToFile_(outfile)
            print ("Clipboard file created.")

    else:
        print ("No clipboard image data was retrieved.")
        print ("These types were available:")
        print (pb.types())

if __name__ == "__main__":
    main()

Answer 2

You can bind a non-occupied shortcut like cmd+shift+E to the menu item Export as PDF... in Keyboard preferences under app shortcuts.

You'll anyway use cmd+S to save it, just one more key gives this exported as PDF. You might need to remove .png from the file name.

If resizing is a step somewhere, and is very frequent, as pointed out by @benwiggy, using shortcuts for Export.. is a good idea. You might want to see in some .plist files about setting the default format to be PDF, not PNG.

If it is not so frequent, you can use Spotlight to find the file, use cmd+enter to reveal it in Finder and crop it using cmd+shift+A (Show markup toolbar). Then mark the rectangle and use cmd+K to crop and save it.

Answer 3

Please make sure you have a backup and know how to use it or reverse this. There is a kind comment explaining they have seen issues. I have done this many times on many OS up to and including Catalina here, but YMMV.

Map Command + S to Export as PDF... in Keyboard Shortcuts to change the default save format.

Same as with Pages or most other apps Apple has a menu item for this option. You could get fancier and just make an automator script to pull the clipboard contents and save as PDF and skip invoking Preview, and needing to press Command N as well, but remapping the S command is the easy fix you can do today.